Hydrocarbon-producing wells are often stimulated by hydraulic fracturing operations, wherein proppants may be used to hold open or “prop” open fractures created during high-pressure pumping. Once the pumping-induced pressure is removed, proppants may prop open fractures in the rock formation and thus preclude the fracture from closing. As a result, the amount of formation surface area exposed to the well bore is increased, enhancing hydrocarbon recovery rates.
In some examples, a hydraulic fracturing operation may comprise pumping a hydraulic fracturing fluid comprising a carrier fluid and a proppant through a wellbore into a subterranean formation. The high pressure may cause the formation to fracture and may allow the fracturing fluid to enter the fractures created in the formation. In some instances, it may be advantageous to use a micro-proppant to prop open micro-fractures created in the formation. The micro-proppant may aid in additional hydrocarbon recovery by propping open small fractures not accessible by larger-sized proppants. A fracturing fluid comprising a micro-proppant and a large-size proppant may expose more formation surface area to the wellbore than fracturing solely with large-size proppant.
While micro-proppants may allow access to natural and micro-factures which are not accessible by using larger-sized proppant, the use of micro-proppants may present some challenges. By way of example, the micro-proppants may undesirably flocculate and fall out of solution. The micro-proppants may comprise a charged surface which may unfavorably interact with other micro-proppant particles or additives in the fracturing fluid. For example a fracturing fluid may comprise a carrier fluid, a micro-proppant with a negative surface charge, and a friction reducer with a positive surface charge. Micro-proppants may be provided in a dispersion. The opposite charges of the micro-proppant and friction reducer may cause the micro-proppant dispersion to become unstable and may cause the micro-proppant to flocculate and settle out of the fracturing fluid. Examples of other factors that may influence micro-proppant dispersion stability in a fracturing fluid include the net surface charge of the micro-proppant and additives, polymer charge density and molecular weight (polymer bridging), concentration of ions in solution (electrostatic screening), micro-proppant concentration, temperature, and carrier fluid rheology, among others.